1. Technical Field
The present invention relates to a power switch for electrical appliances, and more particularly to an on/off control circuit for a soft touch type power switch having momentary contact points.
2. Related Art
Presently, most power switches for switching on/off power supplies used in electrical appliances adopt some push button type switch for easy operation and refined sensibilities. In particular, push button type power switches operated in a soft touch manner are effective in use with home appliances, for example, televisions, VCRs, remote controls, portable computers, etc., since they are in harmony with other function switches or alphanumeric keys using soft touch type push button switches.
In conventional power switches, there is a normal state in which the power switches are not pressed, and the signal supplied to the appliance connected to the power switch is maintained at a predetermined positive voltage. This maintains the appliance in the power-off state. On the other hand, if the power switch is pressed by the user of the appliance, the supply line is altered so that power is applied to the appliance. Once such a power switch of the prior art is pressed again, the appliance is toggled to the power-off state.
A problem with this prior art power switch resides in the fact that the appliance is toggled to a power on or off state whenever the switch is pressed. Thus, erroneous or mischievous pressing of the power switch will result in undesirable change of state of the appliance, with possible disruption to the functioning of the appliance or even possible damage thereto.
The following patents are considered to be representative of the prior art relative to power switches, and disclose arrangements and techniques which are burdened by the disadvantages discussed above: U.S. Pat. No. 5,432,387 to Kogure et al., entitled Power Source Voltage Supply Controlling apparatus, U.S. Pat. No. 5,293,011 to Mokert, entitled Power Lockout Device, U.S. Pat. No. 5,196,731 to Abe et al., entitled Power On/Off Circuit With Lock Function, U.S. Pat. No. 4,689,492 to Peteuil, entitled Switching Circuit, U.S. Pat. No. 4,642,753 to Easthill, entitled Domestic Electrical Appliance, U.S. Pat. No. 4,559,456 to Yamamoto et al., entitled Battery Powered Electric Appliance, U.S. Pat. No. 4,362,954 to Cotton, entitled Power-Up Control For Microprocessor Based Appliance, U.S. Pat. No. 4,314,307 to Sivahop et al., entitled Electro Mechanical Sensor Power Up Circuit, U.S. Pat. No. 4,095,067 to LaScola, entitled Appliance Switch, U.S. Pat. No. 4,068,276 to Pintell, entitled Protective System For Electrical Appliances, and U.S. Pat. No. 4,002,956 to Minor et al., entitled Automatic Electronic Lock Off System For An Appliance.